commondialog problems

The first time in I can view all 20 dat files in the specified folder, select one, and view it.
the second time in, I get ONLY the previous dat file and NO OTHER dat files are showing.
I am using a command button to clear the screen as well as the commondialog.value to " ", but this is not the answer. How do I clear the field, go back and select another dat file and view it. Will your answer allow me to view all 20 dat files, one at a time ?